This invention relates to a modular electrical resistance heating element and particularly relates to a hair comb or pick for most effectively utilizing the heating element of the present invention.
Heating hair combing instruments have been suggested in the past because of their usefulness in drying, curling or straightening hair fibers for cosmetic purposes. Electrically heated hair combing instruments have, in general, been of two basic types.
In some cases, such as shown in U.S. Pat. Nos. 2,648,757 and 3,742,964, the backbone of the comb or the handle of the comb is heated and the heat is transferred into the teeth by thermal conduction. Others have devised hair combing instruments such as those shown in U.S. Pat. No. 1,034,859 and 3,760,821, which extends individual resistance heating elements into each comb tooth.
The first example which calls for heating the backbone of the comb and allowing the heat to be transfered to the teeth by conduction has proved to be impractical for a comb needed for grooming the hair. The concentrated heat at the backbone of the comb must be a high temperature in order for enough heat to conduct to the teeth and be effective. This provides for an unbalanced temperature condition making the backbone of the comb a high temperature and the teeth at a lower temperature.
When the teeth are made hot enough to groom or straighten the hair, the backbone is at a sufficiently higher temperature and will occasionally burn and damage the hair.
The heat rise time is also very slow because of the large mass of metal the heating element is required to heat. This product is therefore impractical for everyday hair grooming. It is therefore apparent that the heat should be applied directly to the teeth to be effective.
The second example, which calls for installing heating elements into each tooth of a comb or pick by looping one continuous element into each tooth, has also proven impractical. For a hair combing instrument to be an effective tool for combing the hair, the teeth must be narrow or approximately 0.094 inch O.D. or less.
The amount of heat needed in hair grooming is relatively low, so heaters used in the application of hair combs must have the ability to transfer and dissipate heat very rapidly without damaging the hair. Present patents on resistance heating elements such as shown in U.S. Pat. Nos. 4,112,410 and 1,553,342 suggest that an insulative material such as a fibrous, inorganic insulation material or a dry powdered electrical insulator be installed between the heating element and the other sheath and then the unit is swaged down to provide for maximum heat transfer.
Due to the fact that the heating element is embodied with the insulation material between the heater and the outer sheath, and the outer sheath is swaged down onto the insulation, this constitutes for a maximum heat transfer in those type heating elements. However, because the heater wire must raise the temperature of everything in direct contact with it or embodying it, the temperature rise time is relatively slow for the inclosed heating element.
Therefore the outer sheath will be slow in reaching operating temperature and the heat will quickly dissipate when the outer sheath surface is cooled by passing the teeth through a substance such as hair fibers.
The electrical energy needed for converting to heat is relatively low for hair grooming, so therefore the previously mentioned heating element will cause the finished product to have either a slow heat transfer rate and a high dissipation rate or if more energy is applied, it will cause the unit to get too hot for hair grooming purposes.
Therefore there is a need for an electrical resistance heating element which is compatible for combing devices and will provide instantaneous heat transfer.